using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using WandEnhancer.Core.Js;
using WandEnhancer.Models;

namespace WandEnhancer.Core
{
    /// <summary>
    /// Patch definitions. Each entry anchors on something Wand does not rename between builds -
    /// an API endpoint, an IPC channel name or a public method name - and then navigates the
    /// delimiter structure to the edit site. Minified identifiers are read out of the located
    /// region rather than baked into a pattern, so a rebuild does not invalidate a patch.
    /// </summary>
    internal static class EnhancerConfig
    {
        /// <summary>Locates the edits a patch must make, or null when the anchor is absent from this file.</summary>
        public delegate JsEdit[] PatchLocator(JsCursor js);

        public sealed class PatchEntry
        {
            public string Name { get; set; }
            public PatchLocator Locate { get; set; }
            public string[] CandidateFileNames { get; set; }
            public string[] SearchHints { get; set; }

            /// <summary>Marks the patch optional: builds without these strings lack the feature entirely.</summary>
            public string[] CapabilityHints { get; set; }

            public bool Applied { get; set; }
            public bool CapabilityDetected { get; set; }

            public bool IsOptional => CapabilityHints != null && CapabilityHints.Length > 0;

            /// <summary>True once the patch is applied, or once a scan proved the feature is absent.</summary>
            public bool IsResolved => Applied || (IsOptional && !CapabilityDetected);
        }

        public static Dictionary<EPatchType, PatchEntry[]> GetInstance()
        {
            return new Dictionary<EPatchType, PatchEntry[]>
            {
                {
                    EPatchType.ActivatePro,
                    new[]
                    {
                        new PatchEntry
                        {
                            Name = "getUserAccount",
                            SearchHints = new[] { "getUserAccount(" },
                            Locate = js => ForceProSubscription(js, "getUserAccount")
                        },
                        new PatchEntry
                        {
                            Name = "setAccountWandBrandExperience",
                            SearchHints = new[] { "setAccountWandBrandExperience(" },
                            CapabilityHints = new[] { "/v3/account/brand_experience_wand" },
                            Locate = js => ForceProSubscription(js, "setAccountWandBrandExperience")
                        },
                        new PatchEntry
                        {
                            // Changing language returns a fresh account object that would otherwise
                            // overwrite the patched subscription in the store.
                            Name = "setAccountLanguage",
                            SearchHints = new[] { "setAccountLanguage(" },
                            Locate = js => ForceProSubscription(js, "setAccountLanguage")
                        },
                        new PatchEntry
                        {
                            // Catches every path that dispatches ACTION_SET_ACCOUNT without going
                            // through the account API methods above (refresh, push, profile edits).
                            Name = "setAccountReducer",
                            SearchHints = new[] { "ACTION_SET_ACCOUNT" },
                            Locate = LocateAccountReducer
                        },
                        new PatchEntry
                        {
                            // Wand's own phone pairing performs a server-side device handoff that
                            // signs this desktop session out. The injected panel does not use it.
                            Name = "disableNativeRemotePairing",
                            SearchHints = new[] { "requestRemoteAuthCode" },
                            Locate = js => Edits(js.FindFunction("requestRemoteAuthCode")?
                                .ReplaceBody(PatchPayload.Load("disable-native-pairing")))
                        }
                    }
                },
                {
                    EPatchType.DisableUpdates,
                    new[]
                    {
                        new PatchEntry
                        {
                            Name = "disableUpdateCheck",
                            CandidateFileNames = new[] { "index.js" },
                            SearchHints = new[] { "ACTION_CHECK_FOR_UPDATE" },
                            Locate = LocateUpdateHandler
                        }
                    }
                },
                {
                    EPatchType.DevToolsOnF12,
                    new[]
                    {
                        new PatchEntry
                        {
                            // Hooked in the main process: the renderer's keydown dispatcher is
                            // reshaped on every Wand release, the Electron app API is not.
                            Name = "devToolsBeforeInputEvent",
                            CandidateFileNames = new[] { "index.js" },
                            SearchHints = new[] { "whenReady().then(" },
                            Locate = LocateDevToolsHook
                        }
                    }
                },
                {
                    EPatchType.RemoteWebPanelPreview,
                    new[]
                    {
                        new PatchEntry
                        {
                            Name = "remoteBridgeMainBoot",
                            CandidateFileNames = new[] { "index.js" },
                            SearchHints = new[] { "whenReady().then(run)" },
                            Locate = LocateBridgeBoot
                        },
                        new PatchEntry
                        {
                            Name = "remoteBridgeReset",
                            SearchHints = new[] { "client-state" },
                            Locate = LocateBridgeReset
                        },
                        new PatchEntry
                        {
                            Name = "remoteBridgeSyncSnapshot",
                            SearchHints = new[] { "client-state" },
                            Locate = LocateBridgeSync
                        },
                        new PatchEntry
                        {
                            Name = "remoteBridgeBindHandler",
                            SearchHints = new[] { "setCurrentTrainer(" },
                            Locate = LocateBridgeBindHandler
                        },
                        new PatchEntry
                        {
                            Name = "remoteBridgeValueDelta",
                            SearchHints = new[] { "client-value-changed" },
                            Locate = LocateBridgeValueDelta
                        }
                    }
                }
            };
        }

        /// <summary>Wraps the account-returning promise so the resolved account always reports an active subscription.</summary>
        private static JsEdit[] ForceProSubscription(JsCursor js, string methodName)
        {
            return Edits(js.FindFunction(methodName)?.WrapReturn(PatchPayload.Load("pro-subscription")));
        }

        private static JsEdit[] LocateAccountReducer(JsCursor js)
        {
            int anchor = js.IndexOf("\"ACTION_SET_ACCOUNT\"");
            var reducer = anchor < 0 ? null : js.FindFunctionAfter(anchor);
            if (reducer == null)
            {
                return null;
            }

            // The payload's ${account} survives PatchPayload untouched and is resolved by the
            // regex replacement below, which is what carries the original identifier through.
            return Edits(reducer.ReplaceInBody(
                @"account:\s*(?<account>[\w$]+)",
                PatchPayload.Load("pro-account-reducer")));
        }

        private static JsEdit[] LocateUpdateHandler(JsCursor js)
        {
            int callOpen = js.FindCall("registerHandler", "\"ACTION_CHECK_FOR_UPDATE\"");
            if (callOpen < 0)
            {
                return null;
            }

            return Edits(new JsEdit(callOpen + 1, js.MatchClose(callOpen), PatchPayload.Load("disable-updates")));
        }

        private static JsEdit[] LocateDevToolsHook(JsCursor js)
        {
            var match = WhenReady.Match(js.Text);
            if (!match.Success)
            {
                return null;
            }

            var payload = PatchPayload.Load("devtools-f12", "app", match.Groups["app"].Value);
            return Edits(new JsEdit(match.Index, match.Index, payload));
        }

        private static JsEdit[] LocateBridgeBoot(JsCursor js)
        {
            var match = WhenReadyThenRun.Match(js.Text);
            if (!match.Success)
            {
                return null;
            }

            var payload = PatchPayload.Load("remote-bridge-boot", "app", match.Groups["app"].Value);
            return Edits(new JsEdit(match.Index, match.Index + match.Length, payload));
        }

        /// <summary>Clears the bridge alongside the session fields the reset method already nulls out.</summary>
        private static JsEdit[] LocateBridgeReset(JsCursor js)
        {
            var sync = FindClientStateMethod(js);
            var reset = sync == null ? null : js.FunctionEndingAt(js.SkipWhitespaceBack(sync.Start - 1));
            if (reset == null || reset.Body.IndexOf("Date.now()", StringComparison.Ordinal) < 0)
            {
                return null;
            }

            return Edits(reset.InsertAtEnd(PatchPayload.Load("remote-bridge-reset")));
        }

        /// <summary>
        /// Mirrors Wand's own client-state payload to the bridge by copying the object literal
        /// verbatim, so fields Wand adds or drops between builds carry over untouched.
        /// </summary>
        private static JsEdit[] LocateBridgeSync(JsCursor js)
        {
            int sendOpen = js.FindCall("send", "\"client-state\"");
            if (sendOpen < 0)
            {
                return null;
            }

            var method = js.EnclosingFunction(sendOpen);
            int snapshotOpen = js.IndexOf("{", sendOpen);
            int snapshotClose = js.MatchClose(snapshotOpen);
            if (method == null || snapshotOpen < 0 || snapshotClose < 0)
            {
                throw new Exception("client-state payload object could not be located");
            }

            // Prettified builds leave a trailing comma inside the literal; appending after it
            // would produce an illegal hole.
            string snapshot = js.Text.Substring(snapshotOpen + 1, snapshotClose - snapshotOpen - 1)
                .Trim()
                .TrimEnd(',');

            var payload = PatchPayload.Load(
                "remote-bridge-sync",
                "snapshot", snapshot,
                "trainer", method.Resolve(@"this\.(?<trainer>#[\w$]+)\s*\?\.\s*getMetadata", "trainer"),
                "metadata", method.Resolve(@"getMetadata\(\s*(?<metadata>[\w$]+\.[\w$]+)\s*\)", "metadata"));

            var edits = new List<JsEdit> { new JsEdit(js.MatchClose(sendOpen) + 1, payload) };
            edits.AddRange(HoistConnectedGuard(js, sendOpen));
            return edits.ToArray();
        }

        /// <summary>
        /// Some builds wrap the whole snapshot method in <c>if (status === Connected)</c>. The bridge
        /// must publish regardless of Wand's own remote status, so the guard is moved onto the send
        /// itself, leaving the block - and the locals the payload reads - intact.
        /// </summary>
        private static IEnumerable<JsEdit> HoistConnectedGuard(JsCursor js, int sendOpen)
        {
            int blockOpen = js.EnclosingOpener(sendOpen, '{');
            int closeParen = blockOpen < 0 ? -1 : js.SkipWhitespaceBack(blockOpen - 1);
            if (closeParen < 0 || js.Text[closeParen] != ')')
            {
                yield break;
            }

            var stack = js.OpenerStack(closeParen);
            if (stack.Count == 0 || js.NameBefore(stack[0]) != "if")
            {
                yield break;
            }

            int openParen = stack[0];
            string test = js.Text.Substring(openParen + 1, closeParen - openParen - 1);

            // Only the connection guard may be hoisted. A nested unrelated `if` would otherwise
            // have its condition moved onto the send, and an `else` branch would be orphaned by
            // turning the block into a bare one.
            if (test.IndexOf("this.status", StringComparison.Ordinal) < 0 || HasElseBranch(js, blockOpen))
            {
                yield break;
            }

            int guardStart = js.SkipWhitespaceBack(openParen - 1) - 1;

            int calleeStart = sendOpen;
            while (calleeStart > 0 && IsCalleeChar(js.Text[calleeStart - 1]))
            {
                calleeStart--;
            }

            yield return new JsEdit(calleeStart, calleeStart, $"({test})&&");
            yield return new JsEdit(guardStart, blockOpen, string.Empty);
        }

        private static bool HasElseBranch(JsCursor js, int blockOpen)
        {
            int afterBlock = js.SkipWhitespaceForward(js.MatchClose(blockOpen) + 1);
            return string.CompareOrdinal(js.Text, afterBlock, "else", 0, 4) == 0;
        }

        private static JsEdit[] LocateBridgeBindHandler(JsCursor js)
        {
            var method = js.FindFunction("setCurrentTrainer");
            if (method == null)
            {
                return null;
            }

            // The same call reveals both the active-trainer field and the numeric or enum value
            // Wand uses for a remote-originated write. Wand has sibling call sites for other
            // sources (Overlay), so an ambiguous match would silently bind the wrong one.
            var setValue = MatchExactlyOnce(RemoteSetValue, js.Text, "Remote setValue call");

            return Edits(method.InsertAtStart(PatchPayload.Load(
                "remote-bridge-renderer",
                "trainer", setValue.Groups["trainer"].Value,
                "remoteSource", setValue.Groups["source"].Value)));
        }

        private static JsEdit[] LocateBridgeValueDelta(JsCursor js)
        {
            int sendOpen = js.FindCall("send", "\"client-value-changed\"");
            if (sendOpen < 0)
            {
                return null;
            }

            int sendClose = js.MatchClose(sendOpen);
            return Edits(new JsEdit(sendClose + 1, PatchPayload.Load("remote-bridge-value-delta")));
        }

        private static JsFunction FindClientStateMethod(JsCursor js)
        {
            int sendOpen = js.FindCall("send", "\"client-state\"");
            return sendOpen < 0 ? null : js.EnclosingFunction(sendOpen);
        }

        private static JsEdit[] Edits(JsEdit edit)
        {
            return edit == null ? null : new[] { edit };
        }

        private static bool IsCalleeChar(char value)
        {
            return char.IsLetterOrDigit(value) || value == '_' || value == '$' || value == '#'
                   || value == '.' || value == '?';
        }

        /// <summary>Match that must be unambiguous: zero or several hits mean an unsupported build.</summary>
        private static Match MatchExactlyOnce(Regex pattern, string text, string what)
        {
            var match = pattern.Match(text);
            if (!match.Success)
            {
                throw new Exception($"{what} could not be located");
            }

            if (match.NextMatch().Success)
            {
                throw new Exception($"{what} matched more than once; cannot tell which call site is the right one");
            }

            return match;
        }

        private static readonly Regex WhenReady = new Regex(@"(?<app>[\w$]+)\.whenReady\(\)\.then\(");
        private static readonly Regex WhenReadyThenRun = new Regex(@"(?<app>[\w$]+)\.whenReady\(\)\.then\(run\)");
        private static readonly Regex RemoteSetValue =
            new Regex(@"this\.(?<trainer>#[\w$]+)\.setValue\(\s*e\.name\s*,\s*e\.value\s*,\s*(?<source>[^,]+?)\s*,");
    }
}