package commandkit

import (
	"errors"
	"io"
	"strings"
)

// Severity classifies a nonterminal provider diagnostic. Terminal failure
// context belongs in an Outcome explanation instead.
type Severity string

const (
	// SeverityInfo marks informational content.
	SeverityInfo Severity = "info"
	// SeverityWarning marks a concern that does not fail the operation.
	SeverityWarning Severity = "warning"
	// SeverityDebug marks diagnostic detail for debug output.
	SeverityDebug Severity = "debug"
	// SeverityProgress marks progress information.
	SeverityProgress Severity = "progress"
)

// OutcomeKind classifies the result of a command invocation.
type OutcomeKind string

const (
	// OutcomeSuccess indicates that the operation completed successfully.
	OutcomeSuccess OutcomeKind = "success"
	// OutcomeUsage indicates invalid command syntax or declared input.
	OutcomeUsage OutcomeKind = "usage"
	// OutcomeOperational indicates an operational failure.
	OutcomeOperational OutcomeKind = "operational"
	// OutcomeDomain indicates a result classified by application domain logic.
	OutcomeDomain OutcomeKind = "domain"
)

// DeliveryState describes the result of presenting content to a destination.
type DeliveryState uint8

const (
	// DeliveryNone indicates that no content was submitted to the destination.
	DeliveryNone DeliveryState = iota
	// DeliverySuppressed indicates that all submitted content was intentionally hidden.
	DeliverySuppressed
	// DeliveryComplete indicates that all requested delivery completed.
	DeliveryComplete
	// DeliveryIncomplete indicates that rendering or destination writing failed.
	DeliveryIncomplete
)

// ErrReporterClosed is returned when a reporting handle is used after
// invocation finalization.
var ErrReporterClosed = errors.New("reporter is closed")

// Detail renders optional content to the writer supplied by the reporter.
// Use that writer only during the callback. A callback must not submit another
// message, queue deferred work, or start another rendering operation through
// the same invocation's reporter.
type Detail func(io.Writer) error

// Explanation contains terminal content for a failed outcome. CommandKit
// presents it during invocation finalization, including in quiet mode.
type Explanation struct {
	// Message is the literal opening text.
	Message string
	// Details render additional content in order.
	Details []Detail
}

// PresentationResult records output and diagnostic delivery observations
// populated by CommandKit during invocation finalization. It is not a message
// submission path or a transcript.
type PresentationResult struct {
	// Output records delivery to the result destination.
	Output DeliveryResult
	// Diagnostics records delivery to the diagnostic destination.
	Diagnostics DeliveryResult
}

// DeliveryResult records rendering and writing errors for one destination.
// The state distinguishes no submitted content, intentionally suppressed
// content, completed delivery, and incomplete delivery. RenderError and
// WriteError retain the first error of their kind for that destination.
type DeliveryResult struct {
	// State summarizes content delivery to the destination.
	State DeliveryState
	// RenderError is the first rendering error for the destination.
	RenderError error
	// WriteError is the first destination write error.
	WriteError error
}

// Diagnostic is passive nonterminal message data returned by a provider. It
// does not emit output or select an invocation outcome; the owning integration
// submits it through the invocation reporter.
//
// Write renders the diagnostic to a supplied writer when the owning integration
// submits it through the invocation reporter. A nil Write function has no detail.
type Diagnostic struct {
	// Severity classifies the diagnostic without depending on a provider library.
	Severity Severity
	// Write renders the diagnostic to the supplied writer.
	Write Detail
}

// Acquired pairs a provider value with independent diagnostics and failure
// context. The owning command chooses how to submit each diagnostic and whether
// to attach the explanation to a failed outcome.
type Acquired[T any] struct {
	// Value is the value returned by the acquisition callback.
	Value T
	// Diagnostics are passive nonterminal messages for the owning command to submit.
	Diagnostics []Diagnostic
	// Explanation provides terminal context if the owning command returns failure.
	Explanation Explanation
}

// Outcome is the classified result of an operation. Constructing or returning
// an outcome does not itself write output; Execute presents its explanation
// during finalization.
//
// Cause records an optional operation error without selecting the outcome or
// generating operator-facing text. Presentation records delivery observations
// separately. Invocation coordination treats a zero Outcome as success with
// status 0. Presentation failures change a success or usage outcome to
// operational status 1; a domain outcome keeps its classification and nonzero
// status, while a zero domain status becomes 1.
type Outcome struct {
	// Kind classifies the result.
	Kind OutcomeKind
	// Status is the suggested process status for this result.
	Status int
	// Domain names the application-defined classification when Kind is OutcomeDomain.
	Domain string
	// Cause is the optional operation error, preserved for caller inspection.
	Cause error
	// Explanation contains terminal content for a failed outcome.
	Explanation Explanation
	// Presentation records delivery observations populated by CommandKit.
	Presentation PresentationResult
}

// Success returns a successful outcome with status 0.
func Success() Outcome {
	return Outcome{Kind: OutcomeSuccess}
}

// Failure returns an operational outcome with status 1 and a terminal
// explanation. The message and details are presented once when the outcome is
// returned from an invocation; an optional operation error can be attached with
// WithCause and is not rendered automatically.
func Failure(message string, details ...Detail) Outcome {
	return Outcome{Kind: OutcomeOperational, Status: 1, Explanation: Explanation{Message: message, Details: cloneDetails(details)}}
}

// Usage returns a usage outcome with status 2 and a terminal explanation. The
// message and details are presented when the outcome is returned from an
// invocation; an optional cause is preserved separately with WithCause.
func Usage(message string, details ...Detail) Outcome {
	return Outcome{Kind: OutcomeUsage, Status: 2, Explanation: Explanation{Message: message, Details: cloneDetails(details)}}
}

// Domain returns an application-domain outcome with the supplied name and
// status. The application owns the classification and status decision.
func Domain(name string, status int) Outcome {
	return Outcome{Kind: OutcomeDomain, Status: status, Domain: name}
}

// WithExplanation returns a copy of the outcome with the supplied terminal
// explanation, replacing any existing explanation. CommandKit presents it once
// during finalization, including in quiet mode.
func (o Outcome) WithExplanation(message string, details ...Detail) Outcome {
	o.Explanation = Explanation{Message: message, Details: cloneDetails(details)}
	return o
}

// WithCause returns a copy of the outcome with the supplied optional operation
// cause. The cause is preserved for caller inspection and does not select an
// outcome or generate operator-facing text.
func (o Outcome) WithCause(cause error) Outcome {
	o.Cause = cause
	return o
}

func cloneDetails(details []Detail) []Detail {
	if details == nil {
		return nil
	}
	return append([]Detail{}, details...)
}

// MessageDiagnostic returns passive diagnostic data that writes message followed
// by a newline when submitted through a reporter.
func MessageDiagnostic(severity Severity, message string) Diagnostic {
	return Diagnostic{
		Severity: severity,
		Write: func(w io.Writer) error {
			_, err := io.WriteString(w, strings.TrimSuffix(message, "\n")+"\n")
			return err
		},
	}
}