// shellApp.c — DVX Shell application loading, lifecycle, and reaping
//
// Manages DXE app loading via dlopen/dlsym, resource tracking through
// sCurrentAppId, and clean teardown of both callback-only and main-loop apps.

#include "shellApp.h"
#include "dvxDialog.h"

#include <dlfcn.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

// ============================================================
// Module state
// ============================================================

// Fixed-size app slot table. Using a static array (not dynamic) because:
// 1. The number of concurrent apps is bounded by available DOS memory
// 2. App IDs are slot indices, so a fixed array gives O(1) lookup
// 3. No fragmentation concerns from repeated malloc/free cycles
// Slot 0 is reserved (represents the shell itself); apps use slots 1..31.
static ShellAppT sApps[SHELL_MAX_APPS];
int32_t          sCurrentAppId = 0;

// ============================================================
// Prototypes
// ============================================================

static int32_t    allocSlot(void);
static void       appTaskWrapper(void *arg);
static const char *baseName(const char *path);
void              shellAppInit(void);
void              shellForceKillApp(AppContextT *ctx, ShellAppT *app);
ShellAppT        *shellGetApp(int32_t appId);
int32_t           shellLoadApp(AppContextT *ctx, const char *path);
void              shellReapApp(AppContextT *ctx, ShellAppT *app);
bool              shellReapApps(AppContextT *ctx);
int32_t           shellRunningAppCount(void);
void              shellTerminateAllApps(AppContextT *ctx);

// ============================================================
// Static helpers
// ============================================================

// Find the first free slot, starting at 1 (slot 0 is the shell).
// Returns the slot index which also serves as the app's unique ID.
// This linear scan is fine for 32 slots.
static int32_t allocSlot(void) {
    for (int32_t i = 1; i < SHELL_MAX_APPS; i++) {
        if (sApps[i].state == AppStateFreeE) {
            return i;
        }
    }

    return -1;
}


// Task entry point for main-loop apps. Runs in its own cooperative task.
// Sets sCurrentAppId before calling the app's entry point so that any
// GUI resources created during the app's lifetime are tagged with the
// correct owner. When the app's main loop returns (normal exit), the
// state is set to Terminating so the shell's main loop will reap it.
//
// If the app crashes (signal), the signal handler longjmps to main and
// this function never completes — the task is killed externally via
// shellForceKillApp + tsKill.
static void appTaskWrapper(void *arg) {
    ShellAppT *app = (ShellAppT *)arg;

    sCurrentAppId = app->appId;
    app->entryFn(&app->dxeCtx);
    sCurrentAppId = 0;

    // App returned from its main loop — mark for reaping
    app->state = AppStateTerminatingE;
}


static const char *baseName(const char *path) {
    const char *slash = strrchr(path, '/');

    if (!slash) {
        slash = strrchr(path, '\\');
    }

    return slash ? slash + 1 : path;
}

// ============================================================
// Public API (alphabetical)
// ============================================================

void shellAppInit(void) {
    memset(sApps, 0, sizeof(sApps));
}


// Forcible kill — no shutdown hook is called. Used for crashed apps
// (where running more app code would be unsafe) and for "End Task".
// Cleanup order matters: windows first (removes them from the compositor),
// then the task (frees the stack), then the DXE handle (unmaps the code).
// If we closed the DXE first, destroying windows could call into unmapped
// callback code and crash the shell.
void shellForceKillApp(AppContextT *ctx, ShellAppT *app) {
    if (!app || app->state == AppStateFreeE) {
        return;
    }

    // Destroy all windows belonging to this app. Walk backwards because
    // dvxDestroyWindow removes the window from the stack, shifting indices.
    for (int32_t i = ctx->stack.count - 1; i >= 0; i--) {
        if (ctx->stack.windows[i]->appId == app->appId) {
            dvxDestroyWindow(ctx, ctx->stack.windows[i]);
        }
    }

    // Kill the task if it has one
    if (app->hasMainLoop && app->mainTaskId > 0) {
        if (tsGetState(app->mainTaskId) != TaskStateTerminated) {
            tsKill(app->mainTaskId);
        }
    }

    // Close the DXE
    if (app->dxeHandle) {
        dlclose(app->dxeHandle);
        app->dxeHandle = NULL;
    }

    app->state = AppStateFreeE;
    shellLog("Shell: force-killed app '%s'", app->name);
}


ShellAppT *shellGetApp(int32_t appId) {
    if (appId < 1 || appId >= SHELL_MAX_APPS) {
        return NULL;
    }

    if (sApps[appId].state == AppStateFreeE) {
        return NULL;
    }

    return &sApps[appId];
}


// Load a DXE app: dlopen the module, resolve symbols, set up context, launch.
// DXE3 is DJGPP's dynamic linking system — similar to dlopen/dlsym on Unix.
// Each .app file is a DXE3 shared object that exports _appDescriptor and
// _appMain (and optionally _appShutdown). The leading underscore is the
// COFF symbol convention; DJGPP's dlsym expects it.
int32_t shellLoadApp(AppContextT *ctx, const char *path) {
    // Allocate a slot
    int32_t id = allocSlot();

    if (id < 0) {
        dvxMessageBox(ctx, "Error", "Maximum number of applications reached.", MB_OK | MB_ICONERROR);
        return -1;
    }

    // Load the DXE
    void *handle = dlopen(path, RTLD_GLOBAL);

    if (!handle) {
        char msg[512];
        snprintf(msg, sizeof(msg), "Failed to load %s:\n%s", baseName(path), dlerror());
        dvxMessageBox(ctx, "Error", msg, MB_OK | MB_ICONERROR);
        return -1;
    }

    // Look up required symbols
    AppDescriptorT *desc = (AppDescriptorT *)dlsym(handle, "_appDescriptor");

    if (!desc) {
        char msg[256];
        snprintf(msg, sizeof(msg), "%s: missing appDescriptor", baseName(path));
        dvxMessageBox(ctx, "Error", msg, MB_OK | MB_ICONERROR);
        dlclose(handle);
        return -1;
    }

    int32_t (*entry)(DxeAppContextT *) = (int32_t (*)(DxeAppContextT *))dlsym(handle, "_appMain");

    if (!entry) {
        char msg[256];
        snprintf(msg, sizeof(msg), "%s: missing appMain", baseName(path));
        dvxMessageBox(ctx, "Error", msg, MB_OK | MB_ICONERROR);
        dlclose(handle);
        return -1;
    }

    void (*shutdown)(void) = (void (*)(void))dlsym(handle, "_appShutdown");

    // Fill in the app slot
    ShellAppT *app = &sApps[id];
    memset(app, 0, sizeof(*app));

    app->appId = id;
    snprintf(app->name, SHELL_APP_NAME_MAX, "%s", desc->name);
    snprintf(app->path, sizeof(app->path), "%s", path);
    app->dxeHandle   = handle;
    app->hasMainLoop  = desc->hasMainLoop;
    app->entryFn      = entry;
    app->shutdownFn   = shutdown;
    app->state        = AppStateLoadedE;

    // Set up the context passed to appMain
    app->dxeCtx.shellCtx = ctx;
    app->dxeCtx.appId    = id;

    // Derive app directory from path (everything up to last '/' or '\').
    // This lets apps load resources relative to their own location rather
    // than the shell's working directory. Handles both Unix and DOS path
    // separators because DJGPP accepts either.
    snprintf(app->dxeCtx.appDir, sizeof(app->dxeCtx.appDir), "%s", path);

    char *lastSlash = strrchr(app->dxeCtx.appDir, '/');
    char *lastBack  = strrchr(app->dxeCtx.appDir, '\\');

    if (lastBack > lastSlash) {
        lastSlash = lastBack;
    }

    if (lastSlash) {
        *lastSlash = '\0';
    } else {
        app->dxeCtx.appDir[0] = '.';
        app->dxeCtx.appDir[1] = '\0';
    }

    // Launch. Set sCurrentAppId before any app code runs so that window
    // creation wrappers stamp the correct owner. Reset to 0 afterward so
    // shell-initiated operations (e.g., message boxes) aren't misattributed.
    sCurrentAppId = id;

    if (desc->hasMainLoop) {
        uint32_t stackSize = desc->stackSize > 0 ? (uint32_t)desc->stackSize : TS_DEFAULT_STACK_SIZE;
        int32_t  priority  = desc->priority;

        int32_t taskId = tsCreate(desc->name, appTaskWrapper, app, stackSize, priority);

        if (taskId < 0) {
            sCurrentAppId = 0;
            dvxMessageBox(ctx, "Error", "Failed to create task for application.", MB_OK | MB_ICONERROR);
            dlclose(handle);
            app->state = AppStateFreeE;
            return -1;
        }

        app->mainTaskId = (uint32_t)taskId;
    } else {
        // Callback-only: call entry directly in task 0 (the shell).
        // The app creates its windows and returns. From this point on,
        // the app lives entirely through event callbacks dispatched by
        // the shell's dvxUpdate loop. No separate task or stack needed.
        app->entryFn(&app->dxeCtx);
    }

    sCurrentAppId = 0;
    app->state = AppStateRunningE;

    shellLog("Shell: loaded '%s' (id=%ld, mainLoop=%s, entry=0x%08lx, desc=0x%08lx)", app->name, (long)id, app->hasMainLoop ? "yes" : "no", (unsigned long)entry, (unsigned long)desc);
    return id;
}


// Graceful reap — called from shellReapApps when an app has reached
// the Terminating state. Unlike forceKill, this calls the app's
// shutdown hook (if provided) giving it a chance to save state, close
// files, etc. The sCurrentAppId is set during the shutdown call so
// any final resource operations are attributed correctly.
void shellReapApp(AppContextT *ctx, ShellAppT *app) {
    if (!app || app->state == AppStateFreeE) {
        return;
    }

    // Call shutdown hook if present
    if (app->shutdownFn) {
        sCurrentAppId = app->appId;
        app->shutdownFn();
        sCurrentAppId = 0;
    }

    // Destroy all windows belonging to this app
    for (int32_t i = ctx->stack.count - 1; i >= 0; i--) {
        if (ctx->stack.windows[i]->appId == app->appId) {
            dvxDestroyWindow(ctx, ctx->stack.windows[i]);
        }
    }

    // Kill the task if it has one and it's still alive
    if (app->hasMainLoop && app->mainTaskId > 0) {
        if (tsGetState(app->mainTaskId) != TaskStateTerminated) {
            tsKill(app->mainTaskId);
        }
    }

    // Close the DXE
    if (app->dxeHandle) {
        dlclose(app->dxeHandle);
        app->dxeHandle = NULL;
    }

    shellLog("Shell: reaped app '%s'", app->name);
    app->state = AppStateFreeE;
}


// Called every frame from the shell's main loop. Scans for apps that have
// entered the Terminating state (either their task returned or their last
// window was closed) and cleans them up. The deferred-reap design avoids
// destroying resources in the middle of a callback chain — the app marks
// itself for termination, and cleanup happens at a safe top-level point.
bool shellReapApps(AppContextT *ctx) {
    bool reaped = false;

    for (int32_t i = 1; i < SHELL_MAX_APPS; i++) {
        if (sApps[i].state == AppStateTerminatingE) {
            shellReapApp(ctx, &sApps[i]);
            reaped = true;
        }
    }

    return reaped;
}


int32_t shellRunningAppCount(void) {
    int32_t count = 0;

    for (int32_t i = 1; i < SHELL_MAX_APPS; i++) {
        if (sApps[i].state == AppStateRunningE || sApps[i].state == AppStateLoadedE) {
            count++;
        }
    }

    return count;
}


void shellTerminateAllApps(AppContextT *ctx) {
    for (int32_t i = 1; i < SHELL_MAX_APPS; i++) {
        if (sApps[i].state != AppStateFreeE) {
            shellForceKillApp(ctx, &sApps[i]);
        }
    }
}