package commandkit

import (
	"bytes"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"unicode"
)

func newConfigShowCommand[C any](suite ConfigSuite[C]) (Command, error) {
	spec := CommandSpec[configInput[C]]{
		Name:    string(ConfigShow),
		Summary: "Show effective configuration as YAML.",
		Flags:   configInputFlags(suite, "yaml"),
		CheckInput: func(input configInput[C]) error {
			_, err := preflightConfig(suite, input, ConfigShow)
			return err
		},
		Run: func(invocation Invocation, input configInput[C]) Outcome {
			return runConfigShow(invocation, suite, input)
		},
	}
	return NewCommand(spec)
}

type effectiveDocument struct {
	name string
	view ConfigView
}

func runConfigShow[C any](invocation Invocation, suite ConfigSuite[C], input configInput[C]) Outcome {
	if err := invocation.Context.Err(); err != nil {
		return Failure(err)
	}
	scopeNames, err := selectConfigScopes(suite, input, ConfigShow)
	if err != nil {
		return Failure(err)
	}
	contexts := contextsForScopes(suite, input, scopeNames)
	documents := make([]effectiveDocument, 0, len(scopeNames))
	diagnostics := make([]Diagnostic, 0)
	for _, name := range scopeNames {
		scope, ok := findConfigScope(suite.Scopes, name)
		if !ok || scope.Acquire == nil {
			return showFailure(fmt.Errorf("configuration scope %q has no acquisition callback", name), diagnostics, false)
		}
		if err := invocation.Context.Err(); err != nil {
			return showFailure(err, diagnostics, false)
		}
		acquired, acquireErr := scope.Acquire(invocation.Context, ConfigRequest{Operation: ConfigShow, Selection: input.Selection}, contexts[name])
		diagnostics = append(diagnostics, acquired.Diagnostics...)
		if acquireErr != nil {
			return showFailure(acquireErr, diagnostics, false)
		}
		if err := invocation.Context.Err(); err != nil {
			return showFailure(err, diagnostics, false)
		}

		if acquired.Value.Effective == nil {
			return showFailure(fmt.Errorf("configuration scope %q did not provide an effective configuration writer", name), diagnostics, false)
		}
		documents = append(documents, effectiveDocument{name: name, view: acquired.Value})
	}

	if err := invocation.Context.Err(); err != nil {
		return showFailure(err, diagnostics, false)
	}
	if len(documents) == 1 && input.Scope != "all" {
		checked := &checkedWriter{writer: invocation.Streams.Out}
		renderErr := documents[0].view.Effective.WriteEffective(checked)
		if checked.failure != nil {
			if renderErr == nil {
				renderErr = checked.failure
			} else {
				renderErr = errors.Join(renderErr, checked.failure)
			}
		}
		if renderErr != nil {
			outcome := showFailure(renderErr, diagnostics, true)
			outcome.DeliveryError = checked.failure
			return outcome
		}
		outcome := Success()
		outcome.Diagnostics = diagnostics
		return outcome
	}

	written := false
	for index, document := range documents {
		if err := invocation.Context.Err(); err != nil {
			return showFailure(err, diagnostics, written)
		}
		var native bytes.Buffer
		if err := document.view.Effective.WriteEffective(&native); err != nil {
			return showFailure(err, diagnostics, written)
		}
		if err := invocation.Context.Err(); err != nil {
			return showFailure(err, diagnostics, written)
		}
		if index > 0 && hasYAMLDirective(native.Bytes()) {
			if err := writeReport(invocation.Streams.Out, []byte("...\n")); err != nil {
				outcome := showFailure(err, diagnostics, true)
				outcome.DeliveryError = err
				return outcome
			}
		}
		framed := frameEffectiveYAML(document.name, native.Bytes())
		if index < len(documents)-1 && len(framed) > 0 && framed[len(framed)-1] != '\n' {
			framed = append(framed, '\n')
		}
		if err := writeReport(invocation.Streams.Out, framed); err != nil {
			outcome := showFailure(err, diagnostics, true)
			outcome.DeliveryError = err
			return outcome
		}
		written = true
	}
	outcome := Success()
	outcome.Diagnostics = diagnostics
	return outcome
}

func hasYAMLDirective(native []byte) bool {
	lines := bytes.Split(native, []byte("\n"))
	for _, line := range lines {
		trimmed := bytes.TrimSpace(line)
		if isYAMLDocumentStart(string(trimmed)) {
			return false
		}
		if bytes.HasPrefix(trimmed, []byte("%YAML ")) || bytes.HasPrefix(trimmed, []byte("%TAG ")) {
			return true
		}
		if len(trimmed) > 0 && trimmed[0] != '#' {
			return false
		}
	}
	return false
}

func frameEffectiveYAML(scope string, native []byte) []byte {
	label := scope
	for _, r := range scope {
		if unicode.IsControl(r) {
			label = strconv.Quote(scope)
			break
		}
	}
	comment := []byte("# scope: " + label + "\n")
	lines := bytes.SplitAfter(native, []byte("\n"))
	position := 0
	preambleEnd := 0
	hasDirective := false
	for _, line := range lines {
		trimmed := strings.TrimSpace(string(line))
		if isYAMLDocumentStart(trimmed) {
			out := make([]byte, 0, len(native)+len(comment))
			// Inline content may be a block scalar; place the label before
			// its marker rather than interrupting the native value.
			content := strings.TrimSpace(strings.TrimPrefix(trimmed, "---"))
			if content != "" && !strings.HasPrefix(content, "#") {
				out = append(out, native[:position]...)
				out = append(out, comment...)
				out = append(out, native[position:]...)
				return out
			}
			out = append(out, native[:position+len(line)]...)
			if len(line) > 0 && line[len(line)-1] != '\n' {
				out = append(out, '\n')
			}
			out = append(out, comment...)
			out = append(out, native[position+len(line):]...)
			return out
		}
		if strings.HasPrefix(trimmed, "%YAML ") || strings.HasPrefix(trimmed, "%TAG ") {
			hasDirective = true
		}
		if trimmed == "" || strings.HasPrefix(trimmed, "#") || strings.HasPrefix(trimmed, "%YAML ") || strings.HasPrefix(trimmed, "%TAG ") {
			preambleEnd = position + len(line)
		} else {
			break
		}
		position += len(line)
	}
	result := make([]byte, 0, len(native)+len(comment)+5)
	if hasDirective {
		result = append(result, native[:preambleEnd]...)
	}
	result = append(result, []byte("---\n")...)
	result = append(result, comment...)
	if hasDirective {
		result = append(result, native[preambleEnd:]...)
	} else {
		result = append(result, native...)
	}
	return result
}

func showFailure(cause error, diagnostics []Diagnostic, reportStarted bool) Outcome {
	outcome := Failure(cause)
	outcome.Diagnostics = diagnostics
	outcome.ReportIncomplete = reportStarted
	return outcome
}

func isYAMLDocumentStart(line string) bool {
	return strings.HasPrefix(line, "---") && (len(line) == 3 || line[3] == ' ' || line[3] == '\t')
}