package shell

import (
    "bytes"
    "fmt"
    "io"
    "os"
    "os/exec"
    "path/filepath"
    "strings"
)

type Shell struct {
    vars     map[string]string
    builtins map[string]func([]string) error
    lastExit int
}

func New() *Shell {
    s := &Shell{
        vars:     map[string]string{},
        lastExit: 0,
    }
    s.initBuiltins()
    s.vars["SHELL"] = "bash-for-windows"
    s.vars["BASH_VERSION"] = "1.0.0"
    s.vars["?"] = "0"
    if pwd, err := os.Getwd(); err == nil {
        s.vars["PWD"] = pwd
    }
    if home, err := os.UserHomeDir(); err == nil {
        s.vars["HOME"] = home
    }
    return s
}

func (s *Shell) Execute(input string) error {
    input = strings.TrimSpace(input)
    if input == "" {
        return nil
    }

    lines := strings.Split(input, "\n")
    for _, line := range lines {
        line = strings.TrimSpace(line)
        if line == "" || strings.HasPrefix(line, "#") {
            continue
        }
        if err := s.executeLine(line); err != nil {
            return err
        }
    }
    return nil
}

func (s *Shell) executeLine(line string) error {
    // Tokenize the line into its components, handling &&, ||, ;
    return s.executeChain(line)
}

// executeChain: parse && / || / ; with left-to-right precedence
func (s *Shell) executeChain(line string) error {
    // Strategy: split by ; first (semicolons always separate), 
    // then by &&/|| within each segment
    segments := splitBySemicolon(line)
    
    for _, seg := range segments {
        seg = strings.TrimSpace(seg)
        if seg == "" {
            continue
        }
        if err := s.executeAndOrList(seg); err != nil {
            // In ; chains, errors in one command don't stop execution
            s.setExitCode(err)
        }
    }
    return nil
}

func splitBySemicolon(line string) []string {
    var parts []string
    current := ""
    inSingle := false
    inDouble := false
    
    for i := 0; i < len(line); i++ {
        c := line[i]
        switch {
        case c == '\'' && !inDouble:
            inSingle = !inSingle
            current += string(c)
        case c == '"' && !inSingle:
            inDouble = !inDouble
            current += string(c)
        case c == ';' && !inSingle && !inDouble:
            parts = append(parts, current)
            current = ""
        default:
            current += string(c)
        }
    }
    if current != "" {
        parts = append(parts, current)
    }
    return parts
}

// executeAndOrList: parse && / || with left-to-right precedence
func (s *Shell) executeAndOrList(line string) error {
    type token struct {
        text string
        op   string // operator BEFORE this token (except first = "")
    }

    var tokens []token
    current := ""
    op := ""
    inSingle := false
    inDouble := false

    for i := 0; i < len(line); i++ {
        c := line[i]
        switch {
        case c == '\'' && !inDouble:
            inSingle = !inSingle
            current += string(c)
        case c == '"' && !inSingle:
            inDouble = !inDouble
            current += string(c)
        case c == '&' && !inSingle && !inDouble:
            if i+1 < len(line) && line[i+1] == '&' {
                if current != "" {
                    tokens = append(tokens, token{current, op})
                    current = ""
                }
                op = "&&"
                i++
            } else {
                current += string(c)
            }
        case c == '|' && !inSingle && !inDouble:
            if i+1 < len(line) && line[i+1] == '|' {
                if current != "" {
                    tokens = append(tokens, token{current, op})
                    current = ""
                }
                op = "||"
                i++
            } else {
                current += string(c)
            }
        default:
            current += string(c)
        }
    }
    if current != "" {
        tokens = append(tokens, token{current, op})
    }

    if len(tokens) == 0 {
        return nil
    }

    var lastErr error
    for i, tok := range tokens {
        cmd := strings.TrimSpace(tok.text)
        if cmd == "" {
            continue
        }

        shouldRun := true
        if i > 0 && tok.op == "&&" {
            shouldRun = (lastErr == nil)
        } else if i > 0 && tok.op == "||" {
            shouldRun = (lastErr != nil)
        }

        if shouldRun {
            err := s.executePipeline(cmd)
            lastErr = err
            s.setExitCode(err)
        }
    }

    return lastErr
}

func (s *Shell) setExitCode(err error) {
    if err != nil {
        s.vars["?"] = "1"
    } else {
        s.vars["?"] = "0"
    }
}

func (s *Shell) executePipeline(input string) error {
    input = strings.TrimSpace(input)
    if input == "" {
        return nil
    }

    if strings.Contains(input, "|") {
        return s.doPipe(input)
    }

    return s.executeCommand(input)
}

func (s *Shell) executeCommand(input string) error {
    parts := s.tokenize(input)
    if len(parts) == 0 {
        return nil
    }

    cmdName := parts[0]
    args := parts[1:]

    if alias, ok := aliases[cmdName]; ok {
        fullCmd := alias
        if len(args) > 0 {
            fullCmd += " " + strings.Join(args, " ")
        }
        return s.Execute(fullCmd)
    }

    if builtin, ok := s.builtins[cmdName]; ok {
        return builtin(args)
    }

    return s.executeExternal(cmdName, args)
}

func (s *Shell) tokenize(input string) []string {
    var tokens []string
    current := ""
    inSingle := false
    inDouble := false

    for i := 0; i < len(input); i++ {
        c := input[i]

        switch {
        case c == '\'' && !inDouble:
            inSingle = !inSingle
        case c == '"' && !inSingle:
            inDouble = !inDouble
        case (c == ' ' || c == '\t') && !inSingle && !inDouble:
            if current != "" {
                tokens = append(tokens, current)
                current = ""
            }
        case c == '=' && !inSingle && !inDouble:
            current += string(c)
        default:
            current += string(c)
        }
    }

    if current != "" {
        tokens = append(tokens, current)
    }

    for i, tok := range tokens {
        if strings.HasPrefix(tok, "$") {
            key := tok[1:]
            if strings.HasPrefix(key, "{") && strings.HasSuffix(key, "}") {
                key = key[1 : len(key)-1]
            }
            if val, ok := s.vars[key]; ok {
                tokens[i] = val
            } else if val := os.Getenv(key); val != "" {
                tokens[i] = val
            }
        }
    }

    varAssignIdx := -1
    for i, tok := range tokens {
        if strings.Contains(tok, "=") && i == 0 {
            eqIdx := strings.Index(tok, "=")
            if eqIdx > 0 && eqIdx < len(tok)-1 {
                name := tok[:eqIdx]
                value := tok[eqIdx+1:]
                s.vars[name] = value
                os.Setenv(name, value)
                varAssignIdx = i
            }
        }
    }
    if varAssignIdx == 0 && len(tokens) > 1 {
        tokens = tokens[1:]
    }

    return tokens
}

func (s *Shell) executeExternal(cmdName string, args []string) error {
    cmdPath := findExecutable(cmdName)
    if cmdPath == "" {
        return fmt.Errorf("%s: command not found", cmdName)
    }

    cmd := exec.Command(cmdPath, args...)
    cmd.Stdin = os.Stdin
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr

    return cmd.Run()
}

func findExecutable(name string) string {
    if _, err := os.Stat(name); err == nil {
        if info, _ := os.Stat(name); info != nil && !info.IsDir() {
            abs, _ := filepath.Abs(name)
            return abs
        }
    }

    path := os.Getenv("PATH")
    for _, dir := range filepath.SplitList(path) {
        fullPath := filepath.Join(dir, name)
        info, err := os.Stat(fullPath)
        if err == nil && !info.IsDir() {
            return fullPath
        }
        fullPathExe := fullPath + ".exe"
        info, err = os.Stat(fullPathExe)
        if err == nil && !info.IsDir() {
            return fullPathExe
        }
    }
    return ""
}

func (s *Shell) doPipe(input string) error {
    commands := strings.Split(input, "|")

    type cmdPart struct {
        name    string
        args    []string
        builtin bool
    }

    var parts []cmdPart
    for _, part := range commands {
        part = strings.TrimSpace(part)
        if part == "" {
            continue
        }
        tokens := s.tokenize(part)
        if len(tokens) == 0 {
            continue
        }
        name := tokens[0]
        _, isBuiltin := s.builtins[name]
        parts = append(parts, cmdPart{name, tokens[1:], isBuiltin})
    }

    if len(parts) == 0 {
        return nil
    }

    var prevOutput []byte

    for i, p := range parts {
        var input []byte
        if i > 0 {
            input = prevOutput
        }

        if p.builtin {
            output, err := s.captureBuiltin(p.name, p.args, input)
            if err != nil {
                // Don't return error, let it pass
                prevOutput = nil
                if i == len(parts)-1 {
                    return err
                }
                continue
            }
            if i == len(parts)-1 {
                fmt.Print(string(output))
            } else {
                prevOutput = output
            }
        } else {
            cmdPath := findExecutable(p.name)
            if cmdPath == "" {
                return fmt.Errorf("%s: command not found", p.name)
            }
            cmd := exec.Command(cmdPath, p.args...)
            cmd.Stderr = os.Stderr

            if i == 0 && len(input) == 0 {
                cmd.Stdin = os.Stdin
            } else if len(input) > 0 {
                stdin, _ := cmd.StdinPipe()
                go func() {
                    stdin.Write(input)
                    stdin.Close()
                }()
            }

            if i == len(parts)-1 {
                cmd.Stdout = os.Stdout
                if err := cmd.Run(); err != nil {
                    return err
                }
            } else {
                output, err := cmd.Output()
                if err != nil {
                    return err
                }
                prevOutput = output
            }
        }
    }

    return nil
}

func (s *Shell) captureBuiltin(name string, args []string, input []byte) ([]byte, error) {
    oldStdout := os.Stdout
    oldStdin := os.Stdin
    r, w, _ := os.Pipe()
    os.Stdout = w

    if len(input) > 0 {
        ir, iw, _ := os.Pipe()
        iw.Write(input)
        iw.Close()
        os.Stdin = ir
        defer ir.Close()
    }

    fn := s.builtins[name]
    err := fn(args)

    w.Close()
    os.Stdout = oldStdout
    os.Stdin = oldStdin

    var buf bytes.Buffer
    io.Copy(&buf, r)
    r.Close()

    return buf.Bytes(), err
}